Biomass means all organic matters which are formed by directly or indirectly using the photosynthesis of green plants, including plants, animals, microbes and excretions and metabolites thereof, and has renewability, low pollution and widespread distribution. In view of energy safety and environment protection, the development and utilization of the biomass have therefore become a strategic key for developing renewable energy sources at present.
The biomass liquefaction technology is an important part of biomass resource utilization and are mainly divided into two classes, i.e., indirect liquefaction and direct liquefaction, wherein the direct liquefaction means directly liquefying the biomass from a solid to a liquid by methods such as hydrolysis and supercritical liquefaction or by introducing hydrogen, inert gas, etc. under the action of a solvent or a catalyst at proper temperature and pressure. The direct biomass liquefaction technologies include pyrolytic liquefaction, catalytic liquefaction, pressurized hydroliquefaction, etc., among which the pressurized hydroliquefaction has high product yield and good product quality, however, the pressurized hydroliquefaction requires harsh reaction conditions and comprises very complicated procedures such as solid material drying, crushing, slurrying, heating, pressurizing, reacting and separation. For example, a process for co-liquefying heavy oil-biomass through hydrogenation is disclosed in a Chinese Patent Document CN103242871A. The process comprises the steps of pre-crushing a dried biomass to obtain a pre-crushed biomass of 40-100 meshes, then, mixing the pre-crushed biomass with a heavy oil to form a slurry, adding a catalyst and a vulcanizing agent into the slurry, then, putting the slurry into a slurry-bed hydrogenation reactor for carrying out hydrothermal cracking reaction by controlling a reaction temperature of 370° C. to 430° C. and a partial pressure of hydrogen to 4 MPa to 8 MPa to obtain a product mixture which was then subjected to fractionation to obtain a fuel oil, chemical raw material and coke.
Although the above process can achieve a conversion rate of the biomass as high as 90 wt % or more and an oil phase yield of about 70 wt %, this technology has a relatively high reaction temperature and a smaller hydrogen partial pressure, and only one liquefaction reaction is carried out, so as to cause a lower reaction efficiency of hydrolysis, cracking, hydrogenation and so on in the liquefaction process, and further result in generation of a large amount of coke and thereby a low liquid yield. Therefore, how to improve the existing biomass liquefaction process to overcome the defects of low reaction efficiency and generation of large amount of coke is a difficult technical problem that needs to be solved by those skilled in the art.